A PART of the spectacular Beijing Olympics opening ceremony was faked, it has emerged.

As the ceremony got under way with a drummed countdown, viewers at home and watching giant screens inside the Bird’s Nest stadium saw a series of giant footprints outlined in fireworks proceed above the city from Tiananmen Square.

What they did not realise was that they were watching computer graphics, digitally inserted into the coverage at the right moment.

The fireworks were there for real, outside the stadium. But those responsible for filming the extravaganza decided beforehand that it would be impossible to capture all 29 footprints from the air.

As a result, only the last footprint, which was visible from the camera stands inside the Bird’s Nest, was captured on film.

The trick was revealed in the Beijing Times. Gao Xiaolong, the head of the visual effects team, said it had taken almost a year to create the 55-second sequence.

Meticulous efforts were made to ensure it was as unnoticeable as possible. The team sought advice from the Beijing meteorological office on how to re-create the hazy effects of the city’s smog at night, and inserted a slight camera-shake effect to simulate filming from a helicopter. “Seeing how it worked out, it was still a bit too bright compared to the actual fireworks,” he said.

“But most of the audience thought it was filmed live – so that was mission accomplished.”

He said the main problem with trying to shoot the real thing was manoeuvring a helicopter to see all 29 footsteps in a row.

One adviser to the Beijing Olympic Committee defended the decision to use make-believe to impress the viewer. “It would have been prohibitive to have tried to film it live,” he said.

“We could not put the helicopter pilot at risk by making him try to follow the firework route.”

A spokeswoman for the committee said the final decision had been made by Beijing Olympic Broadcasting, a joint venture between the International Olympic Committee and local organisers that provides the main “feeds” of all Olympic events to viewers around the world.

“As far as we are concerned, we let off the fireworks. That’s what’s important to us,” she said.

Mr Gao said he was worried that technologically literate viewers who spotted the join might be critical. But the comments received online suggested admiration of the result.